This invention relates to a process for producing a macromolecular compound having a functional group at each end of the molecule. For convenience, such macromolecular compounds are termed .alpha.,.omega.-compounds. They are by definition at least difunctional compounds; when the molecule has more than two ends bearing terminal functional groups it is said to be .alpha.,.omega.-polyfunctional.
According to the prior art, .alpha.,.omega.-polyfunctional macromolecular compounds, also known as functionalised oligomers, are conventionally obtained by two methods, namely direct synthesis and the degradation of high molecular weight macromolecules.
The direct synthesis by polymerisation of oligomers having terminals functional groups has hitherto been extremely difficult to perform, if not impossible. This is because it is only possible when the monomer used polymerises anionically if the initiator is bifunctional. Further, the costs involved in this method of synthesis preclude its application on a commercial scale. Synthesis is difficult if the monomer polymerises radically or cationically.
Hitherto, the degradation of high molecular weight macromolecules has been carried out by the oxidising cleavage of unsaturated macromolecules. In the most commonly used process, ozone is used to attack carbon-carbon double bonds in the macromolecule. However this process is attended by the disadvantage that it is not sufficiently selective and permits the oxidation of sites of the macromolecule other than the double bonds, particularly since in practice the ozone is mixed with oxygen, which can give rise to per-oxidation reactions. In order to try to prevent these extraneous reactions, additives may be introduced which act as inhibitors. Unfortunately, either the additives are consumed, which further increases the cost of the operation, or their effectiveness is inadequate.
.alpha.,.omega.-Polyfunctional macromolecules, i.e. macromolecules containing reactive terminal functions, are highly sought-after products. This is particularly the case with .alpha.,.omega.-difunctional macromolecules which have numerous uses. For example starting from .alpha.,.omega.-difunctionalised polymers or oligomers, it is possible by using polyfunctional crosslinking agents to form three-dimensional macromolecular networks having particularly desirable physico-mechanical properties. In particular, if the molecular weight distribution of the oligomers is fairly narrow, then the distribution of the inter-node intervals of the network is also fairly narrow i.e. the network is fairly tight. It is known that crosslinked products such as these can be expected to have further improved mechanical properties.
Certain .alpha.,.omega.-difunctionalised products are also suitable for use in binders for rocket fuels. Liquid elastomers having a glass transition temperature which is as low as possible are primarily required for this particular application.
The production of trisequential or polysequential copolymers is also a field in which .alpha.,.omega.-difunctionalised oligomers are extremely useful. A disadvantage however is that although polysequential copolymers can be directly synthesised, for example by anionic polymerisation, this process is difficult to carry out on an industrial scale and cannot be used with monomers which, like isobutene, only polymerise cationically. In contrast, trisequential or polysequential copolymers may be obtained from .alpha.,.omega.-difunctional oligomers by the reactions commonly encountered in organic chemistry. For example, it is possible to react .alpha.,.omega.-glycol oligomers with .alpha.,.omega.-acid dichloride oligomers or even to react .alpha.,.omega.-diol oligomers with .alpha.,.omega.-diisocyanate oligomers. A sequential polycondensate is obtained in this way. It is also possible to initiate the polymerisation of a monomer from both ends of a suitably difunctionalised oligomer. In this case, a trisequential copolymer is obtained. Irrespective of the method used to synthesise these sequential copolymers, it can be seen that the starting materials are .alpha.,.omega.-di-functionalised oligomers. It is known that these sequential copolymers show the phenomenon of phase segregation which provides them with interesting physicomechanical properties. In particular, if a trisequential copolymer has a central elastomeric sequence and two terminal plastomeric sequences, or if a sequential copolycondensate has alternate elastomeric and plastomeric sequences, the material obtained will show so-called "thermoplastic elastomer" properties, for which these products are in demand.